Wiring help/question (2 Viewers)

[Crtroopy]

I hope this makes sense.. say i have a circuit with 3 lights (5amps each for a total of 15amps) on it all in a line from the fuse. 1st one is 5 feet from the fuse, 2nd is 10' and the last is 15'. Can i start with 10awg (The calculator i used said 10awg is correct for 15' at 15amp) that runs towards all 3 lights. Once that 10awg reaches the 1st light can I continue after the first light with a lower awg wire since after the 1st light the rest of the run would only be 10amps now for the next 2 lights? And then possibly smaller awg after the 2nd light because the rest of the run to the last light is only 5amps? Almost like plumbing where you can reduce the size of the water line after feeding some fixtures as long as the continued run is sized properly for the remaining fixtures. Any and all help is greatly appreciated.

 

[80t0ylc]

I would say, no. A circuit that has a load of 'x' amps, has that load from source to ground. It's one reason a relay is used for switching high amp circuits. The relay allows a lower amp rated circuit to control a higher amp rated circuit. For example, the switch on the dash that turns on auxilary lights involves running wiring from the dash to the aux lights usually mounted at either end of the vehicle. If the relay is mounted close to the lights, the length for more expensive heavy gauge wire can be reduced. Lighter gauge can be used for the longer run from switch to relay.

 

[Crtroopy]

makes sense, thank you

 

[KLF]

No you shouldn't do this.

I'm assuming you have a 20A fuse on the circuit. Now consider the situation where there is a fault to ground on the 3rd light wire which is much smaller, let's say a 16 ga. The problem is that your protection on that circuit will allow 20A of current, on a much lighter wire that is only rated for about 8-10 amps, so this wire could melt and cause a fire before the fuse will let go.

Remember: the protection device (fuse or circuit breaker) on any circuit should always be the weakest link for the entire circuit.

 

[Crtroopy]

makes sense thank you